[CH3:1][CH2:2][CH2:3][CH2:4][CH:5]([OH:9])[C:6]([OH:8])=[O:7].C(O)(=O)[C@H](C)O.C(OC(=O)C)(=O)C>O>[C:6]([OH:8])(=[O:7])[CH:5]([CH3:4])[OH:9].[OH:9][CH:5]([CH2:4][CH2:3][CH2:2][CH3:1])[C:6]([OH:8])=[O:7]DL-2-Hydroxycaproic acid (1.00 g, 0.0076 moles), and L-lactic acid (4.5 g of a nominally 85% solution in water; 0.043 moles) were placed in a reaction flask equipped with a distillation head and mechanical stirrer. The flask was heated at 110° C. for 6 hours under low vacuum (aspirator) while water was removed. The temperature was then raised to 140° C. for 6 hours. Acetic anhydride (5.16 g; 0.0506 moles) was added to the oligomer, followed by heating at 80° C. for 14 hours. Excess acetic anhydride and acetic acid were distilled off under low vacuum. Tetrahydrofuran/water (15 mL of 85/15; v/v) was added with stirring and heating at 60° C. for 0.5 hours. The bulk of the solvent was removed by vacuum distillation on a rotary evaporator. The resulting crude product was dissolved in chloroform (20 mL). The chloroform solution was washed twice with millipore water (5 mL) and then dried with MgSO4. The mixture was filtered through a "d" fritted glass funnel and the solvent distilled from the oligomer by rotary evaporation. Final traces of solvents were removed under high vacuum (0.4 mmHg) on a Kugelrohr apparatus at 120° C. to provide acetyl-oligo(D,L-2-hydroxycaproic-co-L-lactic acid) with n=7.5 for lactic acid and 1.4 for hydroxycaproic acid, MN =763, and MW =1044.
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